An LED lamp (also known as a bulb or, more generally, an LED lighting product) may be used to replace an incandescent, halogen, or other bulb; the LED lamp provides the same or similar light while consuming less power and providing a longer operational lifetime. One of the difficulties in designing, in particular, halogen-replacement LED lamps is compatibility with the transformers—for example, electronic transformers—that have traditionally powered halogen bulbs. An electronic transformer is a complex electrical circuit and produces a high-frequency (i.e., 100 kHz or greater) AC voltage with a low-frequency (60 Hz) envelope output. An LED lamp powered by the electronic transformer requires a special design to ensure a consistent light output, free of any random or periodic flicker. For example, the electronic transformer has a minimum load requirement; below this minimum load, a portion of the transformer's pulse-train output is either intermittent or entirely cut off. If the load is absent or insufficient, the electronic transformer will enter a low power (or “sleep”) mode until the minimum load requirement is satisfied. When the transformer alternately enters and exits the sleep mode, flickering of the LED lamp may result.
To avoid this problem, some LED lamps use a “bleed” circuit (or a “bleeder”), including, for example, a resistive element, to ensure that the minimum load requirement of the electronic transformer is constantly satisfied. The bleed circuit, however, does not produce light; it merely wastes power, especially if the bleed circuit is implemented during the entire output voltage waveform of the electronic transformer. The bleed circuit, therefore, may not be compatible with a low-power application. Additionally, the time interval during which the bleed circuit is applied to the electronic transformer (the “application time”) may vary if dimming is implemented or different combinations of the electronic transformer and dimmer are used with the LED lamp. A fixed application time may result in unwanted deactivation, or switching on the sleep mode, of the electronic transformer. The application time of the bleed circuit may be determined by continuously monitoring the output voltage waveform of the transformer. However, the necessary monitoring circuitry, if continuously utilized during operation of the LED, will itself undesirably waste power and may generate waste heat that must be dissipated to extend the LED lifetime. Consequently, there is a need for an approach that can determine the appropriate application time of the bleed circuit with minimized power consumption during operation of the LED lamp.